1. Field of the Invention
The present invention relates to novel inorganic pigments/colorants based on rare earths, and more especially, to novel inorganic pigments/colorants based essentially on mixed oxides of rare earths and of divalent metallic elements, exhibiting, on the one hand, very good chromatic characteristics, in particular a remarkable green color and, on the other, the advantage of an absence and/or virtual absence of toxicity.
This invention also relates to a process for the preparation of such pigments and to the use thereof for the coloration of a variety of materials/substrates.
2. Description of the Prior Art
Inorganic pigments/colorants are currently widely employed in many industries, especially in those of paints, plastics and ceramics. For such applications their properties, inter alia, of thermal and/or chemical stability, dispersibility (ability of the product to properly disperse in a given medium), chromaticity, tint strength and covering or masking power are particularly important criteria to be taken into consideration in the selection of a suitable pigment.
Unfortunately, of the inorganic pigments which are suitable for applications such as those indicated above and which are today actually employed on an industrial scale generally comprise metals (cadmium, lead, chromium, cobalt in particular), the use of which is becoming increasingly strictly controlled, or even prohibited, by legislation in many countries; this, at least in part, is due to their toxicity which is widely known to be very high. This is the case as regards red pigments based on cadmium selenide and/or cadmium sulfoselenide, and the case in respect of constituents based on rare-earth sulfides, as well as that of green pigments which present the advantage of, in most instances, containing chromium, particularly in the form of cobalt chromite, of Victoria Green (chromium-based garnets) or chromium(III) oxide.
Thus, serious economic and industrial need continues to exist for substitute inorganic pigments devoid of the above disadvantages and drawbacks.